All the small problems with zfs and omv 2.x did turn me away from using zfs back then

Yes, you are right, there are some small issues with the ZFS plugin, in OMV3 also. But if one is familiar with the basic ZFS CLI commands that should be no big problem.

CLI is no problem. I just try to avoid setups where you always have to fight with the gui and manually added changes.

Like my netatalk 3x upgrade for omv 2. I ended up deinstalling netatalk from omv completely and added the new one. If its too much of a hazzle it makes more sense to skip GUI then and just do it with linux. But thats only if its a pure NAS.
Dont misunderstand me, i love omv. Its just open for me to decide if i move the new array to a bare linux/nas setup or if i upgrade one of my omv machines.